Umbrella



FIG. 1 is an isometric view of an umbrella showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a side elevational view thereof, the front, back and all side elevational views being identical thereto; and,

FIG. 4 is a bottom plan view thereof. 

The ornamental design for an umbrella, as shown and described. 